Always trim for best glide first! No Exceptions!

[tgrayson]

there really isn't all that much excess airspeed and the amount of altitude one gains will likely be minimal.

John Lowry in "Performance of Light Aircraft" did a sample problem for an aircraft zooming after losing an engine during takeoff. He showed that with reasonable assumptions about the time lag in pilot decision-making, the altitude gained in the zoom didn't compensate for the increased drag of the maneuver, so the aircraft experienced a net loss of altitude. When he made superhuman assumptions regarding pilot performance, the net altitude gain was small, slightly under 20 feet. However, that aircraft only had 5 knots of excess airspeed to convert into altitude; clearly an aircraft at cruise might do a lot better. Since he doesn't show his work on the drag calculations, it's hard to extrapolate his conclusions to a cruise scenario. The essence of the problem is that an aircraft zooming will be putting a load factor on the airplane, so the AoA will be higher than normal for every airspeed, resulting in more induced drag.

He also does some calculations regarding how best glide changes in a head/tail wind situation. He shows that for moderate winds (~20 knots), the ±1/2 wind factor is much too large; ±1/4 the wind is more reasonable.

 

[tgrayson]

It just bugs me when people (especially CFI's or military IP's) say "always do this in an airplane" when they really should be saying "always do this in THIS airplane."

There is a fine line to be trod; putting too many things in the "it depends" category slows down pilot performance. If you're going to make a statistically safe choice, best glide is a very logical one. After it is achieved and the pilot has time to think, then he might choose a different speed.

 

[FL900]

It's a 150 with the 150 hp conversion, and when I did the checkout with a CFI, he told me to use about 70 for best glide, and with my limited expierience in this airplane it seems to give pretty good results.

The mental checklist consisted of the usual (Mixture rich, carb heat out, mags both, fuel on, primer in and locked)
My friend who was onboard happens to be a CFI, and he pointed out to me later on that I shouldn't even be running it when practicing engine outs in the pattern. Just trim for best glide, carb heat out, and land.

I haven't read all of the posts in this thread, so I apologize if somebody already said this, but don't John and Martha teach the ABC checklist for engine failure?

A - Airspeed best glide
B - Best landing site selected
C - Cockpit checks (Mixture, carb heat, etc.)

Don't want to come across as an •, but I think you did that backwards. I have always heard and taught that the first priority is airspeed, you can always try to restart once that's done.

Anyway, it looks like you learned that, and I'm glad it was during practice and not the real deal.

 

[avi8tor1983]

A neat little trick I learned from a wise old man,

One thing the FARAMT states is that no airplane should stall at flight idle with full nose up trim. Its true. The thing about a 150, 152 or a 172 is that when you do trim the nose all the way up at flight idle you will be very very close to best glide. Within 2 or 3 knots.

What I always taught my students.

OK Engine Failure!
CFI: Pull the throttle to flight idle
Student: Start trimming nose up (Not quickly of course but swipe, and count one two, next full swipe, etc.) and look for a place to land.

When you hit the stop the student has a TON of time (if at a suitable alt.) to go through the checklists pretty much hands off. Try it! works wonders!

 

[ryan1234]

Now, most of the people on this thread are probably talking about piston aircraft, and probably mostly in regards to Cessnas (or a few of the other common GA brands- Pipers, etc.). I think the take-away is that like almost everything else in aviation there is ALWAYS an exception and your results (and your aircraft's POH) may vary. I think too many CFI's (and military instructors also) teach "always" and "never" when they should be saying "usually" or "rarely/seldom".

Absolutely agree.... nothing beats having good situational awareness...

For example (pertaining airplane to airplane) - there's a certain multi-engine seaplane that if you have an engine failure a pattern altitude or below... you best just start looking for somewhere to land quick and pull the power a bit. Also best is to find the nearest body of water and set her down immediately (so you don't have to lower the gear). Why? Some may ask..... well because both engines draw off the same fuel tank, single engine climb performance is in the negative, it's a STOL airplane.... it cruises slow. It'll bleed energy really fast. You just don't have time to have your head in the cockpit for too long.

All in all it's just best to know the airplane. =.. always, doesn't mean always.

 

[ppragman]

A neat little trick I learned from a wise old man,

One thing the FARAMT states is that no airplane should stall at flight idle with full nose up trim. Its true. The thing about a 150, 152 or a 172 is that when you do trim the nose all the way up at flight idle you will be very very close to best glide. Within 2 or 3 knots.

What I always taught my students.

OK Engine Failure!
CFI: Pull the throttle to flight idle
Student: Start trimming nose up (Not quickly of course but swipe, and count one two, next full swipe, etc.) and look for a place to land.

When you hit the stop the student has a TON of time (if at a suitable alt.) to go through the checklists pretty much hands off. Try it! works wonders!

This doesn't always work with some of the larger piston singles. Cherokee 6s, Cessna 206s/207s, and a few others won't be anywhere near to best glide in certain load configurations at full aft trim.

 

[A150K]

I haven't read all of the posts in this thread, so I apologize if somebody already said this, but don't John and Martha teach the ABC checklist for engine failure?

A - Airspeed best glide
B - Best landing site selected
C - Cockpit checks (Mixture, carb heat, etc.)

Don't want to come across as an •, but I think you did that backwards. I have always heard and taught that the first priority is airspeed, you can always try to restart once that's done.

Anyway, it looks like you learned that, and I'm glad it was during practice and not the real deal.

No offence taken. I did do it backwards :crazy:. I did learn and I will always concentrate on airspeed first from now on. Like my CFI said, "The three most important things during landing are airspeed, airspeed, and airspeed."

 

[cmill]

No offence taken. I did do it backwards :crazy:. I did learn and I will always concentrate on airspeed first from now on. Like my CFI said, "The three most important things during landing are airspeed, airspeed, and airspeed."

Airspeed is important, and i might not be your CFI, but for pete's sake look out the window and dont stare at the airspeed. Aim your nose for the landing spot and do what it takes to get there. You'd be surprised how much you miss while flying by instruments.

 

[MikeD]

And, while we tend to train for the en-route failure, "pitch for best glide" also covers the most dangerous failure, engine failure shortly after takeoff, where a "climb" mentality is likely to result in a smoking hole.

John Lowry in "Performance of Light Aircraft" did a sample problem for an aircraft zooming after losing an engine during takeoff. He showed that with reasonable assumptions about the time lag in pilot decision-making, the altitude gained in the zoom didn't compensate for the increased drag of the maneuver, so the aircraft experienced a net loss of altitude. When he made superhuman assumptions regarding pilot performance, the net altitude gain was small, slightly under 20 feet. However, that aircraft only had 5 knots of excess airspeed to convert into altitude; clearly an aircraft at cruise might do a lot better. Since he doesn't show his work on the drag calculations, it's hard to extrapolate his conclusions to a cruise scenario. The essence of the problem is that an aircraft zooming will be putting a load factor on the airplane, so the AoA will be higher than normal for every airspeed, resulting in more induced drag.

We would do the same (regarding just holding a pitch and allowing airspeed to bleed off) if we were about 20-30 knots or less above best glide. Pretty much the same reasoning: you are just as likely to jack up the aggressive climb and get way slow, thus negating any advantage it would have given you. In that case, we just accept the additional speed bleeding down as a little extra forward distance. In the "all engine failure immediately following takeoff" scenario we would just eject

Keep in mind too, and it's something that civilians don't consider for obvious reasons and isn't being considered here in the quoted discussions either, that for many aircraft, commencing a zoom climb following an all-engine failure after takeoff where a flameout landing isn't an option, isn't at all for any aircraft or landing performance. Zooming is done to initiate a positive rate of climb, however slight, to give the ejection seat the best chance of saving you......ie- setting up the ejection seat for success. Understand that "zero/zero" (zero airspeed, zero altitude) ejection seats are only zero/zero while on the ground. Airborne, any combination bank or descending velocity vector are all factors that negatively affect ejection seat performance, and are factors that the seat needs more altitude to overcome. At low altitude, this means that terra-firma may arrive before your good-chute does, or worse, before seat-man separation does. It's imperative to help the seat help you, when that time arises to give the plane back to the taxpayers.

 

[fish314]

Keep in mind too, and it's something that civilians don't consider for obvious reasons and isn't being considered here in the quoted discussions either, that for many aircraft, commencing a zoom climb following an all-engine failure after takeoff where a flameout landing isn't an option, isn't at all for any aircraft or landing performance. Zooming is done to initiate a positive rate of climb, however slight, to give the ejection seat the best chance of saving you......ie- setting up the ejection seat for success. Understand that "zero/zero" (zero airspeed, zero altitude) ejection seats are only zero/zero while on the ground. Airborne, any combination bank or descending velocity vector are all factors that negatively affect ejection seat performance, and are factors that the seat needs more altitude to overcome. At low altitude, this means that terra-firma may arrive before your good-chute does, or worse, before seat-man separation does. It's imperative to help the seat help you, when that time arises to give the plane back to the taxpayers.

True dat. The old tweet seat wasn't ever zero/zero, so you had to always give it a pretty good margin of speed and altitude to work with. Of course, with that old bird you wouldn't even try to dead-stick it in (at least not per the flight manual) unless you were already VERY low (like 200' AGL or below with 100 knots or less). Basically, right off of the runway.


I also liked Tgray's point. While it is true that there are very few, if ANY, "ALWAYS" situations in flying... if the only answer is always "it depends" that doesn't give a student a whole lot to work with either. I usually try to go with, "here's what the dash one (POH, flight manual, regulation, etc...) says about that..."

 

[tgrayson]

Zooming is done to initiate a positive rate of climb, however slight, to give the ejection seat the best chance of saving you

I'm reminded of the old story about the woman cutting off the ends of the roast before baking because her mother did. Copying the behavior of a military or airline pilot under the assumption that it represents "best practice" is foolish until you understand why they do what they do.

 

[SteveC]

I'm reminded of the old story about the woman cutting off the ends of the roast before baking because her mother did.

It would be even better if she bought a smaller pan to justify the practice.